Pomati Francesco, Shurin Jonathan B, Andersen Ken H, Tellenbach Christoph, Barton Andrew D
Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
Institute of Integrative Biology, ETH-Zurich, Zurich, Switzerland.
Front Microbiol. 2020 Jan 22;10:3155. doi: 10.3389/fmicb.2019.03155. eCollection 2019.
Biomass distribution among size classes follows a power law where the Log-abundance of taxa scales to Log-size with a slope that responds to environmental abiotic and biotic conditions. The interactions between ecological mechanisms controlling the slope of locally realized size-abundance relationships (SAR) are however not well understood. Here we tested how warming, nutrient levels, and grazing affect the slope of phytoplankton community SARs in decadal time-series from eight Swiss lakes of the peri-alpine region, which underwent environmental forcing due to climate change and oligotrophication. We expected rising temperature to have a negative effect on slope (favoring small phytoplankton), and increasing nutrient levels and grazing pressure to have a positive effect (benefiting large phytoplankton). Using a random forest approach to extract robust patterns from the noisy data, we found that the effects of temperature (direct and indirect through water column stability), nutrient availability (phosphorus and total biomass), and large herbivore (copepods and daphnids) grazing and selectivity on slope were non-linear and interactive. Increasing water temperature or total grazing pressure, and decreasing phosphorus levels, had a positive effect on slope (favoring large phytoplankton, which are predominantly mixotrophic in the lake dataset). Our results therefore showed patterns that were opposite to the expected long-term effects of temperature and nutrient levels, and support a paradigm in which (i) small phototrophic phytoplankton appear to be favored under high nutrients levels, low temperature and low grazing, and (ii) large mixotrophic algae are favored under oligotrophic conditions when temperature and grazing pressure are high. The effects of temperature were stronger under nutrient limitation, and the effects of nutrients and grazing were stronger at high temperature. Our study shows that the phytoplankton local SARs in lakes respond to both the independent and the interactive effects of resources, grazing and water temperature in a complex, unexpected way, and observations from long-term studies can deviate significantly from general theoretical expectations.
不同大小类别的生物量分布遵循幂律，其中分类单元的对数丰度与对数大小呈比例关系，其斜率受环境非生物和生物条件的影响。然而，控制局部实现的大小-丰度关系（SAR）斜率的生态机制之间的相互作用尚未得到很好的理解。在这里，我们测试了变暖、营养水平和放牧如何影响来自阿尔卑斯山周边地区八个瑞士湖泊的十年时间序列中浮游植物群落SAR的斜率，这些湖泊由于气候变化和贫营养化而受到环境胁迫。我们预计温度升高会对斜率产生负面影响（有利于小型浮游植物），而营养水平和放牧压力增加会产生正面影响（有利于大型浮游植物）。使用随机森林方法从嘈杂的数据中提取稳健的模式，我们发现温度（直接和通过水柱稳定性间接影响）、养分可用性（磷和总生物量）以及大型食草动物（桡足类和枝角类）放牧和选择性对斜率的影响是非线性且相互作用的。水温升高或总放牧压力增加，以及磷水平降低，对斜率有正面影响（有利于大型浮游植物，在湖泊数据集中它们主要是混合营养型）。因此，我们的结果显示出与温度和营养水平预期长期影响相反的模式，并支持一种范式，即（i）在高营养水平、低温和低放牧条件下，小型光合浮游植物似乎更受青睐，以及（ii）在贫营养条件下，当温度和放牧压力较高时，大型混合营养藻类更受青睐。在养分限制下温度的影响更强，而在高温下养分和放牧的影响更强。我们的研究表明，湖泊中浮游植物的局部SAR以复杂、意想不到的方式对资源、放牧和水温的独立和相互作用效应做出反应，长期研究的观察结果可能与一般理论预期有显著偏差。
